The present invention relates to a lithium-ion battery module composed of a plurality of lithium-ion rechargeable battery cells, and to a vehicle and a generating system using such battery modules.
For the prevention of global warming and from concerns that fossil fuels may be exhausted in the near future, expectations have been growing in recent years for large-scale rechargeable battery modules, such as car-mounted rechargeable battery modules used on hybrid cars and electric cars running on a relatively small amount of energy and stationary rechargeable battery modules for smoothing the output of generating systems operating on renewable energies such as solar and wind power. These rechargeable battery modules are required to have both a high output density and a high energy density.
Because of its excellent properties in both the output density and energy density when compared with other battery modules using nickel-metal hydride rechargeable battery cells or lead storage battery cells, a battery module using lithium-ion rechargeable battery cells is expected to expand its car-mounted and stationary applications.
When operated at high output, a large battery module using a combination of a plurality of rechargeable battery cells rises in temperature. When the battery module is installed at locations where heat dissipation is not enough, its battery temperature does not fall as much as it would when installed at other locations, resulting in significant performance deteriorations in the form of capacity drop and resistance increase. To avoid this, a variety of measures are being studied that will enhance an efficiency of cooling the battery module and minimize performance degradations at high temperatures.
JP-A-2006-324112 discloses a battery module so constructed that each air flow path between adjacent flat battery cells is made narrower toward the downstream of cooling air to enhance the cooling efficiency.
JP-A-2005-32701 discloses a lithium-ion battery cell with 0.01%-10% of vinylene carbonate added for improvement of storage characteristics of battery cells at high temperatures. The storage characteristics of battery cells at high temperatures indicate the capability of keeping the battery capacity when the battery is preserved in high temperature condition.
JP-A-2010-170942 discloses a battery module in which the amount of electrolyte in each cell is increased as the cell installation position in the module moves from a low temperature portion to a higher temperature portion in order to reduce variations in performance deteriorations caused by high rate charging and discharging.